1. Field of the Invention
The present invention relates to a transformer, and more particularly, to a transformer applied to a power conversion circuit, which is improved in leakage inductance due to unbalanced coupling between a primary winding and a secondary winding.
2. Description of the Related Art
To date, a variety of power conversion circuits with high power density have been developed. Generally, high-frequency driving is essentially required to increase power density of a switching-mode power conversion circuit.
However, such increase in a switching frequency leads to a switching loss proportional thereto, thereby decreasing overall power conversion efficiency. Therefore, a variety of soft-switching circuits for diminishing the switching loss have been in development.
Representative examples include an active clamp forward converter, an unbalanced driving half-bridge converter, a phase-shift control full bridge converter, and a resonant converter. These circuits perform zero voltage switching by utilizing leakage inductance of a transformer mainly used in power conversion.
The range of the zero voltage switching operation entirely depends on energy of the leakage inductance of the transformer. Therefore, typically, in a case where the leakage inductance of the transformer is small, an additional resonant inductor is connected to the power conversion circuit to assure the range of zero voltage switching. However, the additional resonant inductor connected as described above increases complexity and size of the circuit, while also suffering core and conduction losses.